How to find the index of splitapply
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Yaser Khojah
am 29 Apr. 2019
Kommentiert: Yaser Khojah
am 30 Apr. 2019
I have this code where I split the data into intervals and I look to find the maximum value for each interval as below. I need to find the indexes of the maximum values (Result) as well to collect more information from the original matrix (data). For simplify I created the following example.
x = round(Data(:,18),0);
y = Data(:,17);
[uv,~,idx] = unique(x);
[Result] = splitapply(@max, y, idx);
How can I find the indexes correspond to the Result to get more information from the original data.
Thank you so much for your help.
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Matt J
am 29 Apr. 2019
Bearbeitet: Matt J
am 29 Apr. 2019
The indices within each group or the indices over all of y? If the former,
indices = splitapply(@maxIndex, y, idx);
function out=maxIndex(z)
[~,out]=max(z);
end
7 Kommentare
Matt J
am 30 Apr. 2019
Bearbeitet: Matt J
am 30 Apr. 2019
That is why I asked you at the beginning if you meant, "The indices within each group or the indices over all of y?" If you meant the former, then your first set of results is correct. For example, if I extract all the YY for which idx==1, I obtain,
group=[10,30]
and clearly the maximum over the group occurs at the second element, so indices=2 is the correct output.
However, since It is now clear that you meant "the indices over all of y", here is the solution for that,
XX = [1 2 3 4 5 1 3].';
YY = [10 10 10 20 20 30 20].';
[uv,~,idx] = unique(XX,'stable');
II=(1:numel(XX)).';
S = splitapply(@(xy)maxIndex(xy), [II,YY], idx);
[Result,indices]=deal(S(:,1),S(:,2))
m = [uv, Result, indices]
function out=maxIndex(xy)
[ymax,loc]=max(xy(:,2),[],1);
out=[ymax,xy(loc,1)];
end
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